texts: Plotting Galactic Longitude from 180 to -180

texts:
I made a scatter plot in Python that looks like this:

However, I want galactic longitude, l, to be plotted from 180 to -180 like these graphs from Iorio and Belokurov (2019):

Here is the code for my plot:

sns.set_style("ticks")
sns.set_context("poster")
%matplotlib inline
from matplotlib import pyplot as plt

fig = plt.figure(figsize=(8,5))

ax  = fig.add_subplot(1,1,1, aspect='equal')

ax.scatter(rrl_pm.l, rrl_pm.b, s=1, color='black', alpha=0.1)

ax.set_xlim(0, 360)
ax.set_ylim(-90., 90.)

ax.set_xlabel("l [deg]")
ax.set_ylabel("b [deg]")
textstr = 'N = ' + str(len(rrl_pm.l))
props = dict(boxstyle='round', facecolor='white', alpha=0.5)
ax.text(0.05, 0.95, textstr, transform=ax.transAxes, fontsize=16,
        verticalalignment='top', bbox=props)
plt.title("Scatter Plot of Cleaned Sample of RRLs in Sgr dSph with Spatial AND PM Cuts", fontsize = 16)
plt.savefig("SP-Clean-Spatial-PM.png", dpi = 1000)
plt.show()

If I simply change the xlim to run from 180 to -180 degrees the following graph is produced:

So essentially it only covers half the sky. Why exactly is this the case and what transformations do I need to apply to the galactic longitude for the 2nd plot to "wrap around" and display both sides?


texts: Why would a tidally-locked rocky planet have a first-order spherical harmonic surface temperature distribution?

texts:
The new Letter to Nature Absence of a thick atmosphere on the terrestrial exoplanet LHS 3844b (also ArXiv) analyzes the thermal infrared light curve from the system (about 4.5 to 5.5 um). The planet is assumed to be tidally locked, so lack of asymmetry in the curve is cited as evidence that there is not thermal inertia due to a thick atmosphere, which is what one would expect for this planet.

In the beginning of the paper the authors say:

  We fit the extracted light curve with a simultaneous model of the astrophysical signal and the instrument behavior. The astrophysical signal consisted of a transit model and a first-degree spherical harmonics temperature map to represent the planet’s thermal phase variation.

and later:

  In addition to the spherical harmonics model, we also tested a sinusoid model, which has been commonly used to fit other phase curve data.

I am thinking that the incident flux at a given point on the tidally-locked planet would be

$$I \sim \max (0, \cos(\theta))$$

where $\theta$ is the static zenith angle at a given point, and so the temperature would be something like

$$T \sim I^{1/4} \sim \max (0, \cos(\theta))^{1/4}.$$

Why do they use a first-order spherical harmonic model instead? Is it related to the thermal conductivity of rock?


texts: Why does the path of the moon in an eclipse curve (relative to the sun)

texts:
Reviewing several simulations of the solar eclipse, it is apparent that the path of the moon relative to the sun curves.

Using https://www.timeanddate.com/eclipse/in/usa/kansas-city?iso=20170821 for example, the moon enters at 135 degrees and leaves at 217 degrees direction - that is almost a 90 degree right turn.

Why is the path curved not straight?


texts: I always see galaxies in "disk" shape in pictures. It is like, there is a rotational movement on a plane and the system is balanced by the pulling-in gravitational force which prevents the stars to leap out of the galaxy. What is the physical reason behind this? I have never seen a star in disk shape. A star is nothing but a much much smaller non-solid mass revolving around an axis, just like the galaxies. Does size matter? What makes the difference? Why doesn't a typical galaxy form in a spherical shape rather than a disk shape?


texts: What would a red giant Sun look like from Proxima b?

texts: As of now, Proxima b is the only confirmed planet (or dwarf planet if it didn't clear its orbit - sorry, couldn't resist) around Proxima Centauri, the nearest-known star to the Sun about 4.2 ly away. From that distance, the Sun looks just like an average star in the night sky. Now if the Sun became a red giant, at 256 times its current diameter (if I recall correctly), what would it look like from Proxima b's night sky? On a good telescope, Betelgeuse is recognizable as more than a dot, its surface is visible, that would surely be the case for a red giant Sun too. What would it take to recognize the Sun's surface from the Proxima system? Would the Sun perhaps even cast a visible shadow?


texts: What are the chances of a star colliding with another during a galactic collision?

texts: My specific example for the question is the future collision of the galaxies Milky Way (our own galaxy) and Andromeda in a couple billion years. The star in question is obviously the sun in this case. I want to know the chances of a collision with another star and if it's significant or not.


texts: Why can't we determine the center of the universe

texts: I find this baffling. If we can observe objects moving away from us and each other, than it stands to reason that we can track their paths (relative to each other and ourselves) backward to find a point of origin. In this question answers given suggest that there is no center of the universe. I'm looking for clarification as to why we cannot reverse engineer (to some degree) where this point of origin exists, even if a simple general direction relative to us. I understand that paths may be distorted and skewed by forces as time goes on, but I still don't grasp the concept that we have no way to determine a point of origin or general sense thereof. Help wrapping my inferior brain around this is much appreciated.


texts: What is the bluest narrow band filter mounted on ground based telescopes?

texts:
If we want to check a QSO's lyman alpha narrow band image, could a ground based telescope do that?

I mean under the circumstance that its lyman alpha shifts to 3300A.


texts: Why Comet C/2020 F3 Neowise returns even it's orbit is near- parabolic?

texts:
I have read in Wikipedia about  Comet C/2020 F3 Neowise that it's orbit is near-parabolic. But in another section, it says that it is a non-periodic comet whlith orbital period ranging from 4500 years to 6800 years.
My doubt is how a comet returns back if it is in a parabolic orbit and why it is non-periodic?
Here is the Wikipedia link: https://en.m.wikipedia.org/wiki/C/2020_F3_(NEOWISE)


texts: What does "unremarkable transverse peculiar velocity" mean exactly, and how is it calculated here?

texts:
The abstract of A magnetar parallax (also in MNRAS) contains the following:

Combining our new observations with two archival observations from 2006, we have refined the proper motion and reference position of the magnetar and have measured its annual geometric parallax, the first such measurement for a magnetar. The parallax of 0.40±0.05mas corresponds to a most probable distance 2.5+0.4−0.3kpc for J1810. Our new astrometric results confirm an unremarkable transverse peculiar velocity of ≈200km s−1 for J1810, which is only at the average level among the pulsar population

This reports the first radio astrometric determination of parallax "for a magnetar".
The peculiar phrase "unremarkable transverse peculiar velocity" is vernacularly dissonant, but parenthetical clarifications in the body of the paper help with that:

5 DISCUSSION
As is shown in Table 1, our new proper motion significantly improves on the previous value inferred from the two year-2006 positions; the new distance D = 2.5+0.4−0.3 kpc is consistent with 3.1 ± 0.5 kpc estimated using red clump stars (Durant & van Kerkwijk 2006), while in mild tension with 3.1−4.0 kpc constrained with neutral-hydrogen absorption (Minter et al. 2008), suggesting the  distance to the neutral-hydrogen screen was over-estimated. In models of NS kicks from the electromagnetic rocket effect (Harrison & Tademaru 1975) one might expect magnetars to have higher velocities (Duncan & Thompson 1992). Our new parallax and proper motion corresponds to the transverse velocity vt = 198+29−23 km s−1. Using the Galactic geometric parameters provided by Reid et al. (2019) and assuming a flat rotation curve between J1810 and the Sun, the peculiar velocity (with respect to the neighbourhood of J1810) perpendicular to the line of sight was calculated to be vb = −54 ± 8 km s−1 and vl = −175 ± 26 km s−1. Our refined astrometric results consolidate the conclusion by Helfand et al. (2007) that J1810 has a peculiar velocity typically seen in “normal” pulsars, unless its radial velocity is several times larger than the transverse velocity.

My understanding of that is limited, but I think that "peculiar velocity" is the velocity relative to some larger structure in which it is found and/or believed to be gravitationally associated with, and the "perpendicular peculiar velocity" component comes from some model that includes the assumption of "a flat rotation curve between J1810 and the Sun". But I haven't a clue what that means.
See also Wikipedia's Peculiar_velocity; Galactic_astronomy for a short description.

In galactic astronomy, peculiar motion refers to the motion of an object (usually a star) relative to a Galactic rest frame.

Questions:

How is the transverse component of said peculiar velocity determined here, and what does "a flat rotation curve between J1810 and the Sun" refer to?
Have I got this right, and in general "peculiar velocity" is a velocity relative to some larger structure in which it is found and/or believed to be gravitationally associated with?


texts: Subterranean Oceans On Other Planets/Planetoids: How Do Astronomers Deduce This

texts: Recently I have been looking into planetoids in our asteroid belt and I have found one that caught my interest, Ceres. One of the main points that was said about it was that it had a subterranean ocean. But I'm puzzled as to how astronomers can come to this conclusion. Any explanations would be much appreciated.


texts: Is Jupiter just a super earth with hydrogen atmosphere?

texts: Often I see books which state that Jupiter has a rocky core, if it is true, does it originate from super earth with excessive collection of hydrogen?


texts: Any programme that shows actual planet information?

texts:
I don't know if this question should be here, if it shouldn't just let me know.

My question is, I'm programming in Java and I want to get the actual stats of the planet, like orbit ,actual temperature etc... Is there any method, package in any language that makes this?


texts: Does Oxygen-burning process produce Neon?

texts:
In the book "Horizons_ exploring the universe-Cengage learning (2018)", p200, it states that:

Helium fusion produces carbon, and some of the carbon nuclei absorb helium nuclei to form oxygen. A few of the oxygen nuclei can absorb helium nuclei and form neon and then magnesium.

But when I check Wikipedia for Oxygen-burning process, there doesn't seem to have any steps that will produce Neon, but when I check for Carbon-burning process, two carbon-12 nuclei can fuse to a neon and helium nuclei, so is there an error in the book? Or there are other steps of oxygen burning that will produce neon?


texts: Are we so sure global warming is a result of humans burning fossil fuels?

texts: The Sun is a fiery mass of colliding particles.  We still know very little about what it is.  Could it possibly be the output of the sun fluctuates, like our weather, from one extreme to another.  From hot durations to cold durations and back again. I think global warming is the result of higher amounts of solar energy being released from the Sun; that's why it's getting hotter here.  I believe the question is important to all people on planet Earth, par excellence; is humanity, namely our consumption of fossil fuels, the cause of our predicament?


texts: Could science be lost if a phenomena is observed before predicted?

texts:
An observation could validate the predictions made by a previous theory. If something unpredicted is observed, then a new theory which is compatible with the observation should make predictions which later are confirmed by new observations.

But what if no such new predictions are possible to make? What is the scientific status of a theory which after the fact is only compatible with all data, but which cannot make any new predictions? If it would be considered weak, does this mean that discoveries through observation can actually destroy science?

Is this a valid argument for delaying the construction of better observatories until theories have matured given all existing data? Kind of comparable with the forward planetary protection argument which says that human spaceflight to Mars should wait until it is certain that there's no life there which could go extinct when it meets Earthly life.


texts: How do we know dark matter/dark energy exists?

texts: I've never quite understood the theory behind why dark matter and dark energy exist. I know it has something to do with gravitational pull being stronger than what we calculate it SHOULD be, could someone explain this in more detail?


texts:
Historically astronomy has been the regime of visible light, looking at distant objects in the visible spectrum and later taking photographs in the visible spectrum.
In the past century radio astronomy, infrared astronomy and exploring other bands in the electromagnetic spectrum became feasible.
Over the past decade we have been able to begin doing neutrino astronomy, identifying distant neutrino sources.
Is there any reason that this cannot progress to other particles, I.E. general cosmic ray astronomy?
One could consider a specialized telescope (it would need to be in a satellite) that detects muons only and forms images from muon detection, or perhaps a proton telescope. The idea being to map incoming particles to pixels in an image, and assign a brightness depending on frequency of particles.


texts: Are there ways to determine a star's spectral type without the spectrum itself?

texts: Because of the lack of available data online, I am trying to find other ways to determine an exoplanet's host star's spectral type.


texts: Does the Sun's light travel fast enough to have a straight path to Earth?

texts:
When we travel through space, we use a curved path following an orbit to reach our destinations.

As far as I'm aware, we could take a more straight line approach but it would require much more deltaV (both in reaching the speed and in slowing down when reaching the target to be captured.)
However the path would still be slightly curved because of the curvature of space and because of orbital tracjectory when leaving Earth.
Does the light escaping the Sun move fast enough to follow a straight line path until it hits Earth, or is it curved in those 8 minutes?
What about to somewhere further like Pluto?


texts: What is the farthest blueshifted object to our galaxy?

texts: Is it also roughly the limit where gravity will be able to overcome space expansion? In other words, we can only hope to get to there, or at least see them, in the very far future?


texts:
As I learn, the gravity is caused by the spacetime curvature. Is there any gravitational/magnetic field that really exists around the Earth, or any other planets?

Since the planets/stars rotate, does this cause the space time curvature to twist in the direction of their rotation? If it does then the gravitational pull should also twist the the path of the objects falling(though we may not perceive the curvature of this path, we should be
able to calculate at-least theoretically)


texts: Blowing up an asteroid/comet really potentially worse?

texts:
Often on television shows and in articles I see it mentioned that it'd always be bad to blow up an asteroid or comet because then the energy would just be spread out and cause even more damage.

According to some estimates I've seen around 100 tons (or more) of meteoroids hit the Earth each day. If all of this were combined together into a single asteroid, it could destroy an entire, large city.

Given that alone, it makes it seem to me that it be more logical to take the chance and blow up an asteroid and thereby trim its weight down, causing a lot more to be more easily burnt up on entry, so that when it did hit, it would cause less damage.

Is this logical at all? If my science/math/physics is incorrect, I want to understand why having more burn up by spreading out is worse compared to having it more concentrated and vastly more dangerous.


texts:
I have had an impossible time trying to locate this comet. My lat/long is 38.3/-82.4. My elevation is 705ft.
The application that I'm using shows me exactly where Neowise is supposed to be (North East, best viewed before sunrise around 4:00am, etc.), but I've managed to not locate it once in the last three days at that time. Stayed out for an hour straight each time, starting at 4:00am.
Is it not viewable from my position?


texts: What exactly is this VLA radio image of Jupiter showing?

texts:
This VLA image is beautiful, and instructive, but I don't understand it fully.

This version is from an article in Gizmodo where the credit reads: A radio image of Jupiter captured by the Very Large Array. Image: Imke de Pater, Michael H. Wong, Robert J. Sault and which cites the recent article in Science: Peering through Jupiter’s clouds with radio spectral imaging. However, that paper does not actually show this image.

Another version of the image can be found in Berkeley News: New radio map of Jupiter reveals what’s beneath colorful clouds and gives more information how the image was produced.

  A radio image of Jupiter from the VLA at three wavelengths: 2 cm in blue, 3 cm in gold, and 6 cm in red. A uniform disk has been subtracted to better show the fine banded structure on the planet. The pink glow surrounding the planet is synchrotron radiation produced by spiraling electrons trapped in Jupiter’s magnetic field. Banded details on the planet’s disk probe depths of 30-90 km below the clouds. This image is averaged from 10 hours of VLA data, so the fine details seen in the other maps are smeared here by the planet’s rotation. Image by Imke de Pater, Michael H. Wong (UC Berkeley), Robert J. Sault (Univ. Melbourne).

I would like to know more about how the image was processed. What does it look like before the uniform disk is subtracted - is the radio emission from the region around the planet actually as strong as the planet disk itself, as this image suggests? If there is a reference for this image I'd also like to read it!

In the mean time, it really is beautiful!

The image is sometimes paired with the following image, taken here from Science News.

Since this image resolves lateral detail, I'm guessing it might be the same 10 hours of data, but processed with a moving frame and corrected for distortion as it wraps around during the rotation of the planet, while the global image above is smeared by rotation

Was it? Where can I read more about this?


texts: Can a neutron star ever be less than about 1.44 solar masses (the Chandrasekhar limit)? Why not?

texts:
I learned about the Chandrasekhar limit as being the UPPER limit, in terms of mass, for a white dwarf...
But, I have never heard of a neutron star being BELOW that mass, so I have wondered, recently, if that is also a LOWER limit for neutron stars...
I suppose that the squished-together protons and electrons that the neutron star is made of might lose their 'degeneracy', if the gravitational potential is (or becomes) low enough, and the star might 'poof-out' (or proof back out) to a white dwarf...
Has this ever been known to happen?
Can a neutron star experience Hawking radiation and actually lose mass, like a black hole?
If black holes can, theoretically at least, exist at very small masses as long as they are small enough voluminously (compacted within their Swarzschild or Kerr radii), then why can't neutron stars?


texts:
Would a more significant curvature of spacetime relative to earth (i.e. time on jupiter) effect the aging process? Basically would you age at a slower rate?
Or age faster on the moon?


texts:
I am well aware of one-dimensional stellar models:

The simplest commonly used model of stellar structure is the spherically symmetric quasi-static model, which assumes that a star is in a steady state and that it is spherically symmetric.  It contains four basic first-order differential equations: two represent how matter and pressure vary with radius; two represent how temperature and luminosity vary with radius.

But what if we moved from spherical symmetry to cylindrical symmetry? Did somebody already set up all equations and solve them for general rotational symmetric ellipsoid?
What changes, if we would assume a lemon-shaped or (most interestingly) an egg-shaped star?
What would be the (intutive) results of such a stellar model? I am sure, somebody solved the equations already and I am just missing the appropriate search terms.
References

The mathematics of egg shape gives a brief mathematical background about one of my favorite mathematical objects

Cylindrical symmetry is not as hypothetical as it might sound:

Ashley Strickland wrote for CNN about "Unusual tear-drop shaped, half-pulsating star discovered by amateur astronomers"
WASP-12b is is reviewed by NASA as An egg-shaped planet.

The pre-print by E.C. & L.V. Nolan On isotropic cylindrically symmetric stellar models seems to cover the topic, but is not too intuitive.
Related

Can a donut-shape planet or star be formed?


texts: Would there be any difference for our solarsystem to be not in the Milky Way?

texts: Guessing, the solar system would be taken out of our galaxy of any reason, would there be any difference to the live on earth or even to the mechanics in within our solar system?


texts: Why is the Sun's atmosphere (the corona) so hot?

texts: The visible surface of the Sun is 6000 degrees Celsius but the gas in the solar corona is at least 1 million degrees. What heats the solar corona?


texts: As far as we know, Jupiter's moon Io has the most volcanic activity of any known celestial body. It has the most volcanoes that are active and they're erupting frequently. On Earth (the third planet from the Sun) there's lightning during volcanic eruptions and on Venus (the 2nd planet) there's lightning too, probably also during eruptions. Has any lightning ever been detected during an eruption on Io, or isn't it possible for lightning to occur during eruptions on Io for some reason?


texts: "What was that spot in the sky?" - How to identify satellites

texts:
First of all sorry for my immense ignorance in this matter and for all the stupid things I'll say here.
Yesterday, May 22nd 2017, I removed the telescope from its dusty box1 and decided to watch Jupiter. After about 2 minutes of observation I spotted something across the sky [X-files music in background], it was a little less bright as Jupiter's "Galilean" moons2.
Below you can see an accurate [Windows Paint] reconstruction of the fact I saw in my telescope. The red line indicates the direction of the thing (from right to left outside of the telescope).

Available data to help identify the object:
Time: May 22nd, 2017 @ 22:12 UTC
My position: {
    Lat: 41.720194062015096
    Long: 12.713427287843729
    Sea level: 540 m
    }
Direction: Probably South // The direction of Jupiter from that location at that time (didn't have a compass)
Telescope: {
    Focal length: 700 mm
    Diameter: 60 mm
    Lens: H 20 mm
    }

I only have data of the ISS and Iridium insights on an Android app3 so I am here to ask if there is some tool with which I can identify by myself as many satellites as possible across the sky.
Notes:

Winter is not nice with observers from here
Not visible at naked eye
I can almost certainly say that the "thing" was not the ISS or one of the Iridium satellites

P.s: I will post here what the object was (with reference if possible) as soon as I identify it for curious people like me.


texts: Is the duration of a sidereal year stable?

texts:
According to this essay by Phil Plait, the duration of Earth's sidereal year is 31,558,149 seconds.

Is this figure stable? If I were to meaure Earth's orbit several million (or billions) of years in the past or future, should I expect to see roughly the same duration?

If not, what would be the cause of any change observed?


texts: Minimum Mass Solar Nebulae Scaling Factors

texts:
I'm attempting to build a MMSN, I've been trying for about... a week to get an intuition on the scaling factors for calculating the mass of the disks, I'm not entirely sure how to think about it. I feel as if the concept is extremely simple but that I'm thinking of it incorrectly. Can someone explain what exactly these scaling factors account for and how one would calculate them? I'm not looking for a solution, I'm looking for intuition on how these scaling factors are found.

My understand is that you pick an element, (Fe), and compare that to the solar abundance (does this mean the abundance of Fe in the sun? From there I would look at the abundance of Fe in the cores of the planet and compare them somehow to get some sort of scaling factor. From what I understand Fe makes .14% of the suns mass, so if I know lets say that neptune has a mass of 17m(earth) how would I start finding the scaling factor.

Thanks!


texts: How fast would Earth need to rotate to fling someone off due to centrifugal force?

texts:
If Earth started spinning fast enough, would the centrifugal force eventually overcome Earth's gravity enough enough to fling someone (let's assume 75 kg) into orbit or into space? If so, how fast would it need to spin?

Being that I'm not a scientist, I'm hoping for a simple answer like, "one rotation per xx hours/mins/seconds needed to throw someone off Earth" or something to that effect. Complicated equations and/or jargon is fine for the sciencey types, of course. I just probably won't understand it too much.


texts: Can the order of planets change in a young planetary system?

texts: The Nice model and the Grand Tack model both show that the distance between a planet and its host star can change greatly over time. Is it possible in either of these models for the order of planets to change as well? Or is the order of planets around a star the same as when the planets formed?


texts: What was the orbit of the meteor that impacted the Moon on 2013 September 11?

texts:
On 2013 September 11th, a meteor impacted the Moon leaving a 34-meter crater. So far the only info I've found was from youtube (https://www.youtube.com/watch?v=zCFDkj2JtyA) and this site: http://lroc.sese.asu.edu/posts/810

I'm surprised this doesn't have its own wikipedia article (none that I could find, anyway), and google wasn't helpful either. Is the astronomical world more or less oblivious to this event?

Anyway, the data I'm most interested in is the meteor's orbital trajectory. And also, why would such a small meteor leave a "fireball" for 8 seconds according to the youtube video.


texts: Heavy bombardment - Why has things cooled?

texts:
I was always taught and lead to believe that at the beginning of our solar system, there was a period of heavy bombardment, which is conceivable.

Why has it just stopped and we are at peace from this, and, there is no such things happening today?


texts: How would the barycenter of a double-planet system affect the two planets' surface gravity?

texts: Assuming two similarly sized, tidally locked planets orbit a common barycenter, how would the gravity of the barycenter affect the surface gravity? For example, on the inner sides of the planets, what would be the effect of the multiple gravity centers (the planets' and the barycenter), especially to a being on the surface?


texts:
If I had a long stick that was millions of light years long, and with a width of about the Sun, and I then swiped it through the center of the milky way galaxy, what would the probability be of me hitting a star?

EDIT:

Ignore the speed of light. Assume it is possible to just swipe it through instantaneiously.
Assume that the stars in the galaxy are equally distributed. Obviously if you were to swipe right through the middle you would hit the galactic center.
The purpose of this thought experiment is just to help visualise the density vs size of the galaxy.


texts: Explanation for the first spinning neutron star detected in the Andromeda galaxy?

texts:
A new class of Neutron stars has been found in the Andromeda galaxy (M31), This is the first time a Spinning Neutron star has ever been detected by astronomers in M31. The article states-

“pulsars” can be found in stellar couples, with the neutron star cannibalizing its neighbor. This can lead to the neutron star spinning faster and to pulses of high-energy X-rays from hot gas being funneled down magnetic fields onto the neutron star.

“It could be what we call a ‘peculiar low-mass X-ray binary pulsar’ — in which the companion star is less massive than our Sun — or alternatively an intermediate-mass binary system with a companion of about two solar masses,” said Paolo Esposito of INAF-Istituto di Astrofisica Spaziale e Fisica Cosmica, Milan, Italy.

While the precise nature of the system remains unclear, the data imply that it is unusual and exotic.
http://www.astronomy.com/news/2016/04/andromedas-first-spinning-neutron-star-has-been-found

Question-
  Could the companion of this Spinning Neutron Star not be a star at all but a Black Hole? This might explain the unusual spin and that all neutron stars do not consume other binary companions stars but rather a Black Hole is in the process of consuming the neutron stars.

The Black Hole can devour all of the outer energy of any active star leaving only the dense core of heavy metals that will eventually cool off entirely creating the rouge brown dwarf.
  Supernovae never derived from dying neutron stars but rather from Binary star Collisions.


texts:
Recently some new moons of Jupiter were discovered. However the moons are pretty damn small indeed - only a few kilometers wide. That makes me wonder if they should even be called moons in the first place. The Wikipedia article on natural satellites says there's no clear lower limit (or upper limit for that matter). But if we accept that, then Jupiter already has countless numbers of moons in its ring system, and even the Earth has multiple moons since the International Space Station is a "moon".

What exactly is a moon? Is it really a vague notion of "something that goes around a planet"? If so, why hasn't the IAU clarified what exactly a moon is? They've already done so for planets; it seems natural to do so for moons as well.


texts: What are "non-Keplerian" orbits? What are some familiar examples in our solar system, and can some still be closed?

texts:
This excellent answer to Forms of stellar orbits around the galactic center invokes the following concepts:

non-Keplerian orbits
closed orbits

I have a fairly good idea what these mean and so might many of us, but our ideas may not overlap completely.
For the sake of future stack exchangers and orbiteers, how can we best define these?
Question(s):

What exactly are "non-Keplerian" orbits?
What are some familiar examples of distinctly non-Keplerian orbits in our solar system?
What are closed orbits?
What are some familiar examples of distinctly non-closed orbits in our solar system?
Can some non-Keplerian orbits still be closed?

Included should be the understanding that we're talking about soft limits here; no orbit is exactly Keplerian because gravity goes everywhere (there are no "gravitational dielectrics" or opposite charges for field lines to terminate). But for practical purposes we can treat many orbits as Keplerian for many purposes, and some we can't at all.


texts:
I live in Ahmedabad, in India, with an exact location of about 27.2048° N, 77.4975° E. Currently (as of this writing), it is 20:52 EST. I noticed a red object in the sky.

(Forgive the crude imaging. I took this with my phone camera.)
Now, the brighter object is the moon, and the less shiny object is the red one I saw. I read somewhere that Mars would be visible right now, as it is closer to the Earth.
I also read that Mars and Jupiter appear red, with Jupiter slightly dimmer.
I wanted to know whether the object I just saw was indeed a planet. If so, which one (and how can I identify them)? Or is it just another star that I spotted?


texts: Can stellar black holes cancel each other?

texts: Hypothetical question: when a pair of identical stellar black holes are very close to one another wouldn't the side facing each other experience lower gravitational force? How is this logic un/sound?


texts: How would Earth's climate differ if it's axis were tilted around 90 degrees like Uranus?

texts:
As the title states, what would the effect on Earth's climate be if it's axis were tilted approximately 90 degrees like Uranus?

I'm specifically wondering about the effects on seasons, temperature, and life on Earth.  However, I'm happy to hear about other effects as well.


texts: How fast will the sun grow when it becomes a red giant?

texts: We all know that our sun will become a red giant in a couple of billion years? But how fast will the process be when it starts? Would it be theoretically possible (disregarding the deadly effects of this event) for a human to experience the sun as its present size until it swallows earth?


texts: During what time of the year can Centaurus be seen from Tokyo?

texts:
During exactly what dates of the year can the Centaurus constellation be seen from Tokyo, Japan? And what is the ideal date for viewing it from Tokyo?  I found on a website that it can been seen May-June in New Zealand, best visible at 21:00 (9pm) during May and that the midline is May 20th.

(According to the Japanese Wikipedia page for Centaurus, only from Okinawa can the entire constellation be seen; in Tokyo, apparently only part of it can be seen.)


texts: Factors included in the average density of planets

texts: When the average density for a planet is stated does it incorporate the mass of the atmosphere, when a planet has an atmosphere, or is the mass of the atmosphere ignored?


texts: From which exoplanets is our sun the brightest star on the night sky?

texts: The brightest star on the night sky is Sirius, here in the Earth. But are there any exoplanets, where the brightest star on the night sky is our sun?


texts: Regression line in a colour-colour diagram

texts:
A colour-colour diagram (CCD) like this

compares the difference in magnitudes at different wavelengths. The trend in the pattern of colour-colour comparisons tells us about what type of source the light comes from.

Is there any significance in the best-fit line of the trend? As in, if I did a linear regression of the left plot above, I'd get a gradient of (V-R)/(B-V). I realise that this ratio doesn't have any physical significance in terms of a single source, but is there any value in calculating the best fit line and its slope or regression coefficient? Does it tell us anything about the group of sources it's associated with, or is it just used to calibrate filters, as it states on Wikipedia? The answer to this question doesn't really answer mine.


texts: How often are electron-multiplying CCDs used in telescope focal planes? Will Nancy Grace Roman be the first use in a space telescope?

texts:
Section I. of The Wide Field Infrared Survey Telescope: 100 Hubbles for the 2020s says:

Table 1 summarizes the WFIRST instrument suite, and Figure 1 presents the effective area of the Wide Field Instrument (WFI) as a function of wavelength for the imaging filters, grism, and prism. Minor changes to these specifications are possible as the mission design evolves; in particular, the WFI prism bandpass and resolution and some CGI parameters are still being optimized. Substantial changes are not expected. Both CGI channels have a 1024 x 1024 pixel electron-multiplying CCD (EMCCD) in the focal plane. Three of the five CGI observing modes will be fully commissioned prior to launch; support for the other two modes will be on a best effort basis. The CGI imaging modes can all be used with linear polarizers. WFIRST will operate from a Quasi-Halo orbit around the second Sun-Earth Lagrange point (L2).

For background see Wikipedia's Charge-coupled device; electron-multiplying CCD. Apparently within the silicon there are hundreds of stages of electron multiplication (similar to avalanche photodiodes) each with about a 2% probability of multiplication.
Question(s):

How often are electron-multiplying CCDs used in astronomical telescope focal planes?
Will Nancy Grace Roman be the first use in a space telescope?


texts: State vectors of "interesting" multiple stars

texts:
I'd like to show a demonstration of Runge Kutta integration of real systems using examples of interesting multiple stars, where "interesting" means you can see through a small telescope that they are at least double. I've selected three:

Gamma Andromedae (Almach)
Alpha Geminorum (Castor)
Zeta Ursae Majoris (Mizar and Alcor)

How can I find a state vector (set of relative positions and velocities) - or something similar - for these multiple star systems? An open access link (for everyone) would be great, but a journal reference is fine as well if that's what it takes.

Of course the periods are long and there will be uncertainty - I'd just like to use whatever is known and available, for this demonstration.


texts: How does moonrise/moonset azimuth vary with time?

texts:
In my tenacious attempts to observe moonrise (surprisingly difficult in a poor weather heavily urbanized hilly area with frequent bad smog, with busy work schedule and a bicycle) I was frequently trying to find good observation spots that would provide view to open distant horizon at specific azimuth.

While generally similar moon phases correlated with similar moonrise times I found the azimuth to vary in a way I have a difficult time to put my finger on. Sure there's a roughly monthly cycle of "wobble" between deviating about +/- 30 degrees north or south from "pure east" but while the mechanics of correlation between hour when the Moon is visible from behind the horizon and the degree it's lit by the sun are quite clear to me, the way its - or is it Earth's? - orbital plane is "off" relative to the ecliptic plane and Earth rotation plane eludes me. Could someone provide a sort of guide - preferably something that acts more as help in understanding the mechanics, as opposed to providing raw mathematical solutions, what does this deviation depend on, and how it changes with time?


texts: Where can I find a list of retrograde Milky Way stars?

texts:
I read in papers that the Milky Way contains some retrograde stars (retrograde to the Milky Way rotation). Does anybody know where I can find a list of them, possibly including data on their distance from the Milky way center?
many thanks


texts: If the Mars polar caps were melted, how deep would the oceans be?

texts: If the Martian polar ice caps melted, given a surface temperature and pressure that allow for liquid water, how large would the oceans be? Would they match their ancient glory, or would they be smaller?


texts: Meteors made of differing substances. Will they all burn up?

texts:
If an object enters Earth's atmosphere, what determines whether it burns up or not?

Example

A feather is released from a space-ship 30,000 km away from Earth and falls under the influence of Earth's gravity.

Will it burn up on re-entry or will it float down to the surface unharmed. If it would be unharmed, where is the cutoff point for which objects survive?


texts: Why are there different time estimates for a solar photon to reach the surface of the Sun?

texts:
Some estimates range the photon journey from 10,000 to 170,000 and even millions of years, but only consider the path from the sun's core to its surface. This is called 'Random Walk Problem' and assumes the sun's interior has a constant density and that the 'free path' distance for the photon is about 1cm. 1.
An additional reading pointed that is in the Radiative Zone where most of the 'random walk' occurs. Next, the photon goes to the Convection Zone, which density is less than Radiative Zone, where it has lost most of its energy and shifts to visible light. Photon scattering in the Solar Atmosphere is negligible. [2]
1 https://sunearthday.nasa.gov/2007/locations/ttt_sunlight.php
[2] https://futurism.com/photons-million-year-journey-center-sun
Q. Why such a difference between the estimated travel times? Thank you.
May, 15th
There is a neat lecture on the subject
Principles of Astrophysics & Cosmology -  Professor Jodi Cooley
http://www.physics.smu.edu/cooley/phy3368/lectures/150216_lecture.pdf

Calculate how long it takes a photon to travel from the center of the sun and emerge at its surface.

My quote:
"In reality, there are regions where electron scattering is more prominent and regions where it is less important.  As a result, the typical photon mean free path is 1 mm"


texts: Is the age of the solar system equal to the age of meteorites?

texts:
I've read articles that state the age of the solar system has been determined by measuring the amount of decay of isotopes in some meteorite, which has demonstrated that  the lead isotopes in the meteorite have cooled and locked into place some number of years ago.

However, if a yellow sun can not create heavier elements, wouldn't it be correct to say the age of an meteorite dated this way is how long it's been since the asteroid was ejected from a blue or heavier star? The sun may have started burning many years after that.


texts:
What is the timescale of start of nuclear fusion as T Tauri type star transforms into a Main Sequence star?

Wikipedia article on T Tauri type stars mentions:

  Their central temperatures are too low for hydrogen fusion. Instead, they are powered by gravitational energy released as the stars contract, while moving towards the main sequence, which they reach after about 100 million years.

The mentioned 100 million years is the period of the star being in its stable (well, as stable as the turbulent T Tauri type stars get) state without nuclear fusion. Then, once the fusion starts, we get between 3 million and hundreds of billions years of main sequence, depending on mass of the resulting star.

What I'm interested is how long is the period of transition between the two - ignition of the nuclear reaction - time between "all energy produced by gravitational contraction" and "most of energy produced by nuclear fusion".

I imagine this period could be quite short, and the effect quite rapid and turbulent as the initial fusion increases local temperature (and as result pressure) drastically, leading to conditions conductive for fusion spreading rapidly over the volume which is already on brink of entering the fusion everywhere within the protostar, essentially a nuclear wildfire encompassing the gathered gas, a chain reaction starting.

Am I right in my guess this process is rather rapid? Was it ever observed? Or contrary, does the intensity of the fusion reaction rise gradually and slowly from zero over many millions years of star formation?


texts:
I have a question about the view of the Milky Way that we can see from earth with the naked eye.  I believe this to be light from the stars contained in one of the "arms" of the galaxy.  I had always assumed that, from our vantage point, I was looking outward through one of the arms.  This was based on the appearance of the apparent curvature over the sky above.

However, it occurred to me that this could also be looking in towards the center of the galaxy.  And the fact that it appears to curve around us over the night sky is just an illusion.

Or, perhaps at different times in the year we are alternatively looking inward and then later looking outward.

Can any shed some, errr, light on this?


texts: When the big bang happened and all that exist today came into existence from singularity, how do you determine which part of the universe is the oldest?  Its natural to think that looking back at the center of the universe, we would find the oldest galaxies(not sure if this is true); but isn't there a certain logic that the farthest from the center should have the oldest galaxies?  Is there a proven theory behind where we would find the oldest galaxies? or is this one of those space-time enigmas?


texts: Why levels of radio contours maps are given in mJy/beam and what does it mean?

texts:
I know what a jansky is, but I don't understand what beam (in $\frac{1 Jy}{beam}$) is.
If jansky is a unit of flux density, what kind of unit is $\frac{1 Jy}{beam}$?


texts: When graphing radial velocity measurements, whats the relationship between days and the orbital phase

texts: I graphed the radial velocity measurements for various planets, however, I am able to calculate the RV and the phase but whats the translation between phase and days. I want it to be days vs RV.


texts: What is sonic transition of an astrophysical fluid?

texts: My notes mention sonic transition of a fluid. Is it where the speed of the fluid elements cross the speed of sound in the medium they are located?


texts: The effect of gravitational wave is like tidal forces?

texts:
What would happen if a strong gravitational wave passed through a human body or any other kind of material?

The shape of the human body would change?

Would the human body be distorted apart?

If so, would the person survive?


texts: How would Earth's magnetic field change if the outer core was solid?

texts:
A widely accepted theory for how the Earth's magnetic field is generated is the dynamo theory.  Dynamo theory describes how molten magma convection currents containing metal are locally spun the same direction by Coriolis forces, producing a magnetic field.

If Earth's outer core was solid, this effect would go way.  However, the metals in the interior would still be moving (though all together) due to the Earth's rotation.  Would Earth still produce a magnetic field? If so, how would it compare to our current field?  Would it still help shield the atmosphere from charged particles?


texts: What does the angle between plane of earth's orbit and ecliptic vary between?

texts: What does the angle between the plane of the earth's orbit and the ecliptic (now about 23.5 degrees) vary between, and over what time scale?


texts: I read one of the related questions here, but what i'm curious to know is how do we deflect imminent collision courses of comets, if we detect them at a later stage? I read somewhere else that there are systems which use powerful lasers (radiation pressure) to deflect them, but honestly, i don't understand why something like radiation pressure will work on something travelling at about 40km/s through space, and still manage to cause a large enough deflection. Are there other methods ?


texts: Might someone see changes to the corona during a solar eclipse?

texts:
I've seen many pictures of the corona during a solar eclipse, and the structure and delicacy is amazing. Clearly, the appearance would change over time, depending on the fine details of the solar wind and the structure of the mass shed from the solar surface. I wonder, though: might the appearance, to the unaided eye, change during a single eclipse?

This could actually be treated as two questions (all example durations and times taken from the August 2017 eclipse):

a) Might the corona's appearance visibly change during totality at a single location (a maximum of 2 minutes 40 seconds)?

b) Might the corona's appearance visibly change between the first Earth-wide totality (16:48 UTC, when the Moon's shadow touches down in the Pacific) and the last Earth-wide totality (20:02 UTC, when the Moon's shadow last leaves the Atlantic)?

Searching for solar wind velocities yields a broad range of values, but $400km/s$ seems to be a common value. With the solar diameter being about $1{,}400{,}000km$, that's about a solar diameter per hour, which suggests there will be no visible change at a single location, but there certainly could be changes when viewed across the entire 3+ hours of totality.

So, can we expect changes in the coronal appearance during this eclipse, either at a single location or across the entire eclipse path?


texts:
Solar eclipses on the earth are so spectacular because the moon has roughly the same size as the sun when viewed from the earth's surface. This is an incredible coincidence, and my guess is that it is a very uncommon phenomenon in the universe.

Is it possible to say anything sensible about the likelihood of a planet having a moon and a sun with same apparent size? Is it possible to make an educated guess about how many places in the universe you would be able to see an earth-like solar eclipse?


texts: Mass of black holes compared to parent star

texts:
What is the range of percentage mass of parent star left in a stellar black hole directly after its formation?

What factors determine this number for a specific case?


texts: Is science data from astronomical telescopes analyzed with something analogous to "optical character recognition"?

texts:
Do people manually input the science data from telescopes into databases or does some software automatically collect the data from telescopes and put it in servers and databases?

I'd imagine there's too much data from present-day telescopes that they can collect to handwrite or hand by hand input the data from them into spreadsheets therefore computers do it via machine learning?


texts: Are there heavenly bodies between galaxies?

texts:
I do understand that galaxies were formed in the famous Big Bang. However, I also understand that if such an explosion occurs in empty space it will never form distinct galaxies, it should more or less evenly fill the whole empty space.

Many of these might clot together to form galaxies but I cannot agree that between the void of galaxies there are no other bodies.

Am I missing something?


texts: Real-time position of a distant celestial body

texts:
How might it be possible to determine (via some specific online empemeris or via some well-understood algorithm) the observed position of some distant celestial body (e.g. Betelgeuse)?

To be concrete: suppose I wished to do what any number of mobile phone applications do, i.e. computationally model the observed position of stars and project them onto the screen using GPS coordinates and compass direction, so that an `overlay' of the night sky is produced. Then:

a) Where could I source the relevant data from?

b) What coordinate system would it be best to use?


texts:
Earth's core is a giant liquid iron ball actually. If I know well, the magnetic field of our planet (that protects the surface from some particles comes from the Sun) can exist because as Earth rotates, the liquid iron core also rotates, and it generates a magnetic field.

However, ferromagnetism has strict conditions. How can the liquid and hot core still be ferromagnetic? How is it possible for Earth to have a magnetic field generated by a body that is not even solid?


texts: Did interstellar asteroid Oumuamua pass near other stars?

texts:
"Oumuamua came from the direction of Vega, a bright star in the Lyra constellation. But even at 85,700 miles per hour, it took so long to reach our solar system that Vega wasn't in the same position 300,000 years ago."
CNN.

However, there is information on the motions of stars from ESA's Gaia mission (4 min. youtube with description), so it should be possible to project the motion of Oumuamua back it time to see if it was near any stars. Has anyone done this?


texts: What does Stephen Hawking mean by 'an infinite universe'?

texts:
In the recent $100m search for extra terrestrial life project project, Stephen Hawking is quoted in the following way:

  "We believe that life arose spontaneously on Earth," Hawking said at Monday's news conference, "So in an infinite universe, there must be other occurrences of life."

My understanding is that scientists believe that the universe isn't infinite - there there is a finite number of stars, it's continuously expanding but has a finite size at a given time.

What's Stephen Hawking refering to here?


texts: How do we know that the intrinsic brightness of Cepheid variables corresponds to their period?

texts: As I understand it, beyond parallax the next way of estimating the distance to astronomical objects is by using a relationship between the period and intrinsic luminosity of Cepheid variables.  How do we know that relationship?  Are there some close enough that we used parallax to validate it, or is there a theoretical reason, or something else?


texts: Depth of primary and secondary minimum in a light curve

texts:
How can I explain approximately the same depth of primary and secondary minimum in light curve?

I observe star HD 36486. I tried filters MOST and BRITE.

Is it related with photometric filter? When I change the filter in program for analysis the result is the same.


texts: What is the cause of the variation from high and low mean obliquity periods of Mars?

texts:
It is reasonably well known that Mars has a greater obliquity range than Earth, due to Mars lacking a stabilising influence of a large moon.  However, the Martian obliquity seems to have gone through periods of high and low mean obliquity, as shown in the top chart below:

Image source: Mars Climate Modeling Group

What is the current accepted theory as to why there are periodic high and low mean obliquities on Mars?

(Please note, I am not asking about orbital eccentricity)


texts: Two luminous points disappearing in the sky

texts:
I saw a few days ago two luminous points in the sky, which were quite close (about 1-2 degree of separation between them) and not apparently moving (or to slow to be noticed with the naked eye). The apparent luminosity of these points was close to the one of Jupiter (a bit less maybe, but far more luminous than Saturn).
The luminosities of these points increased a bit and after a few seconds they faded. I guess these were not satellites entering in the shadow of the Earth as they were not moving. And I think that the probability for this to be two meteors falling exactly towards me is quite low...
Any suggestion this might be ?


texts: Does the expansion of space imply an increase in the dimensional volume of objects?

texts: Does the expansion of space only occur in the space between celestial objects or is it effecting the dimensional volume of the objects themselves? In simple terms is my ruler expanding due to the expansion of the universe?


texts: Given that gravity bends the path of light, how confident can we be that galaxies are where they seem to be?

texts:
The widely known phenomenon termed gravitational lensing is believed to curve space, thereby affecting the path followed by light and other electromagnetic waves.

This effect is associated principally with galaxies and galaxy clusters, as it requires considerable mass. But in theory any star or star cluster, or black hole, can have this effect to some degree.

What can we tell for sure about the position of external galaxies, if we are uncertain that their light is actually coming to us along a straight path: i.e. if light follows the curvature of space, and that curvature is not uniform, how can we be sure we are not observing, for example, the light from a single source appearing to us as more than one object.

Can a galaxy appear to be in more than one place in the sky?


texts:
Forgive me if any of my terminology is off I am no physicist but I have wondered about this question for a while.

I have read in various books that if the universe was infinite, and uniformly created the whole sky would be white. This is because in every possible location in the sky there would be a star emitting light. Sort of like pixels, filling a screen.

I thought about this and wondered, doesn't this therefore imply that light is never absorbed by another medium?

What if a distant stars light is absorbed, therefore never reaching earth, giving the illusion that there are less stars?


texts: Questions about time and space (from beginner)

texts:
To be honest my knowledge about astronomy and related physics is close to zero. However, since I studied math a bit, I would like to ask a couple maybe stupid questions, which I am curious about and I don't know who and where to ask.

A) Projection of life

Premises:

As Carl Sagan explained in his "flatlanders" story, we can imagine high-dimension space by making projections into space with lower dimension.
As we learned at elementary school time is the fourth dimension.

Question:

Is it right that what we see/feel in every moment is projection of some 4D reality into our 3D world noticed by our senses.
For example, If my eyes were able to "somehow" see in 4D and I pointed my eyes to a person, would I see that person in all stages of his/her life from birth to death as a single "entity"? In every second we are only a projection of our 4D representation to our 3D world?

B) Parallel realities

Premises:

If we imagine 1D space as a line without ends, 2D space as an unbounded plane and 3D space as an unbounded space, then I could put infinity number of parallel lines into 2D space and infinity number of parallel planes to the 3D space.

I have read that there are at least 10 dimensions.

Questions:

Can I put infinite number of 3D spaces into a single 4D space? If yes, then if we for example chose geographic coordinates of Earth-Italy-Caesena as place and 49 B.C. as time coordinate, we would be probably close to event when Caesar screamed his famous: "alea iacta est".

If we considered that 5th dimension exists and that we could put infinite number of 4D spaces into 5D space, then we would end up with infinite number of parallel realities, in which Caesar did not crossed Rubicon, or did not even exist. Is it right or complete nonsense? Can be somehow proved that this is right/nonsense?


texts: What happens if two galaxies collide very quickly?

texts: What would happen if two galaxies collided very quickly (e.g. at near the speed of light)?  Would they mostly just pass through eachother unscathed, or would there be very energetic collisions that would rip both galaxies apart, or would something else happen?


texts: When was the distance to a star measured for the first time without using parallax?

texts:
This is somewhat of a follow-up to When was the parallax of a star first measured? Once the distance to the nearest stars was determined, it was possible to discover physical properties of stars (such as the relation between intrinsic luminosity and color, or the relation between luminosity and period for Cepheid variables), then use the knowledge of those physical properties to find the distance of stars with no visible parallax.
When was the distance to a star (other than the Sun) determined for the first time with a method other than parallax?


texts: If the axial tilt of Uranus (97°) was caused by a giant impact, then why do its moons orbit around its equator at the same tilt (≈97°)?

texts:
So the most accepted explanation for Uranus' axial tilt is that it once had a normal tilt like the other planets bar Venus (0° to 30°), but then a certain massive object collided with it and flipped it on its side.

But by that logic then shouldn't Uranus' moons be orbiting 0° to 30° relative to the orbital plane? (or whatever mild axial tilt Uranus had before the impact)

If they were formed before when Uranus still had a mild axial tilt then it makes no sense for them to be orbiting directly over present-day Uranus' equator.


texts: How do you create a continuum mask in Python or IDL for a star?

texts: I'm learning how to model stellar spectra using the IDL code, Spectroscopy Made Easy (SME), and its Python counterpart, PySME. Has anyone used these programs before? As you can see from the first attached image, the code has trouble modeling the continuum, which has been normalized. When I try to set a continuum mask by setting wavelength ranges (see second image), the ranges get shifted in the modeling... Apparently in the Valenti & Fischer 2005 paper, a solar spectrum was used and then shifted? Any help with this would be sincerely appreciated.


texts:
How did the Milky Way and Andromeda Galaxy separate before they began their collision course?

I understand that gravity is pulling together the two galaxies, but what separated them in the first place while gravity is pulling them together?

Thank you for your consideration.


texts: Is S2 still the fastest known star in the galaxy?

texts:
Wikipedia's entry for the star S2 says that it has

the fastest known ballistic orbit, reaching speeds exceeding 5,000
km/s (11,000,000 mph, or 1⁄60 the speed of light) and acceleration of
about 1.5 m/s2 (almost one-sixth of Earth's surface gravity).

But the referenced link to the press release Surfing a Black Hole is dated 2002.  Have any stars with faster orbital speeds at perimelasma (periapsis for a black hole orbit) in the 19 years since this press release?  Is it possible that there is a star on an even faster orbital trajectory than S2 or has any such possibility been ruled out?


texts: Is a literal instance of Russell's teapot possible?

texts:
Much has been said about Russell's teapot, and I accept as obvious that a teapot would be too small to be detectable in an orbit around the Sun by any reasonable method today, or by any method that can reasonably be expected to develop in the near future. But how small is "too small"? Is it possible that there are bodies the size of Phobos (or even the Moon) in the orbit around Uranus, for example?
If there is anything I know about the Solar System, it's that the gaps in the distances between planets are huge. How can we be sure that there are no large bodies inside those gaps? I guess our observations are mostly based on (the absence of) gravitational anomalies, but how precise are they? Is the "limit of detectability" smaller for orbits around Sun than for much larger orbits e.g. at Jupiter's distance?


texts: How does NASA's ASTHROS stratospheric telescope compare to its James Webb space telescope?

texts:
In Space SE I've asked Would it have been cheaper and faster to put a James Webb-like Space Telescope on a balloon instead of a rocket?
I linked there to a few news items:

CNET: NASA to send stadium-size balloon skyward to study the cosmos
JPL/NASA News: NASA Mission Will Study the Cosmos With a Stratospheric Balloon Even in 2020 balloons are used for space exploration; Q.E.D.
Scitech Daily: NASA ASTHROS: Stratospheric Balloon the Size of a Football Stadium Will Carry a Cutting-Edge Telescope

Question: But here I'd like to ask about the ASTHROS instrument and how it compares in capability and range of instrumentation compared to the JWST. I know that they both have infrared capabilities and cryogenically cooled instrumentation, but I don't know how their instrumentation or spectral ranges compare.  I'm pretty confident that ASTHROS will not have the same aperture as JWST, but I don't know how much smaller it will be
update: The JPL/NASA News article above intriguingly says:

A gondola beneath the balloon will carry the instrument and the lightweight telescope, which consists of an 8.4-foot (2.5-meter) dish antenna as well as a series of mirrors, lenses, and detectors designed and optimized to capture far-infrared light. Thanks to the dish, ASTHROS tied for the largest telescope to ever fly on a high-altitude balloon. During flight, scientists will be able to precisely control the direction that the telescope points and download the data in real-time using satellite links.


texts: If we could travel far enough would we be able to see a constelation in reverse?

texts:
I am enjoying Orion high in the sky this winter as always. I wondered if I could travel beyond it, say 2730 light years* and turn around, would I see Orion in reverse? If so, what of the neighboring constellations. I know brightnesses would be different but would I recognize the shape?

Happy new year to all.

I chose this number because Alnilam is 1360 light years away so I doubled the distance.

Source: https://www.space.com/3380-constellations.html


texts: What does the Reddening line represents in this U-B vs B-V plot?

texts:
The plot is from this paper (pg-8).
They have also talked(in the same paper) about how central stars from galactic longitude range $20^\circ-80^\circ$ will have a very unusual Reddening line (pg-9). The current plot is for central stars from the galactic longitude range $200^\circ-300^\circ$

The group
of planetary nuclei plotted here are all those occurring in galactic longitudes 200o
-300°.
In the longitude range from 20° to 80° the points fall to the right of the reddening line in
Figure 3 (not plotted). If the latter energy-curves are well-behaved, a very unusual
reddening line would be needed to explain their position in the diagram. This is a puzzling result which is unexplained at present.

My interpretation of Reddening line: It is showing that if we plot real star data where the sample contains all the stars from bluer end to redder end on this U-B vs B-V plot, we will get  the Reddening
line on the plot.
Is this interpretation correct?


texts: Why does the Sun move slower during the solstices?

texts:
A comment under this answer states that the apparent angular speed of the Sun is 8% slower during the solstices. This is rather counter-intuitive, since the rotation speed of the Earth is constant (or close enough for the timescales considered).

Why does the Sun appear to move slower in the sky at the solstices?


texts: Mass of a potential black hole in a binary system

texts:
So I've been given the velocity curve, parallax and apparent magnitude of a star in a binary system with what is potentially a black hole. I've calculated from the apparent magnitude and parallax that the star is a type F5V, which puts the mass at about 1.4 Solar Masses. The velocity curve has an inclination of 90, and oscillates back and forth between +/- 75km/s. There is no data on the companion of this star, just the fact that it could be a black hole. I'm supposed to estimate the mass by numerically approximating a polynomial.
So far I've used this equation

$\frac{M^{3}}{(m+M)^{2}} = \frac{Pv^{2}}{2\pi G}$

where M is the mass of the thing I don't know, m is the mass of the known companion (1.4 solar masses) P is the period (5.59 days) and v is of course the velocity (75km/s)

I got lazy and wrote $\frac{Pv^{2}}{2\pi G}$ as $k$ and arrived at

$M^{3} - kM^{2} - km^{2} = 0$

Using python's optimize library I found the mass of this unkown partner to be about 0.018 solar masses. My question here is where did I go wrong, and if I didn't go wrong anywhere is that a realistic mass for a super small black hole / other very small, dense and invisible object?


texts: How do we know that spacetime is fabric?

texts:
I have started learning about astronomy as it amazes and inspires me.
I have a question. What led us to believe that spacetime is fabric? What is the evidence shows this, and is it considered proven?
If possible Send me the link for research papers so I can learn more.
Please explain in layman's term as I am not a astronomy student but a biology student.
Also let me know books that I can be read.


texts: Why is only one side of the Moon visible from Earth?

texts:
Why do we only ever see the same side of the moon?

If this is to do with gravity are there any variables which mean we might one day see more than we have before?


texts: Information on the star at the centre of the Helix "Eye Of God" Nebula

texts: Can someone please tell me what the mass (or size) of the star at the center of the Helix Nebula is, and how much larger it is than our own star (we call the Sun or Sol).  Also, what is the name of this star?  I cannot find a website that addresses these questions.  I believe I have heard, however, that the star is roughly 100 times larger than our sun.


texts: Does the new moon appear at the same time around the world or in one region last

texts:
My query is basically, say for example if the new moon is seen in the Middle east region, does it mean that it was the day of new moon in sub continental country as well ? You can't have a new moon in India for example the next day scientifically, right ? Please help me understand this with diagrams so I can explain it to others.

To me it doesn't make sense that we will have two consecutive new moons in the same region of the planet. New moon in middle east but new moon in India is on the next day.

I am aware since it's a broad topic so timezone can change the answer so in this question. I am restricting my question to the sighting of the new moon in the same region as in say Moon is sighted in Dubai, doesn't it make sense that India will also have the first day of moon on the same day given that it all falls in the same plane.


texts:
Can't black holes just be super dense objects? They could still be black (having the color of black never really required special physics, after all) and have a really strong gravitational field. If we suspect that it actually absorbs light due to its gravity then it is possible that there is gravity strong enough to capture light, not letting any radiate out when matter falls into this object.

I'm just having a hard time accepting that anything can exist with an infinitely large property as it would lead to infinitely large mass leading to infinitely large forces... that would just destroy the universe infinitely fast, wouldn't it? So I think a supermassive object can be a badass just as well without having to be a singularity.


texts: Do we know a star that is similar to the Sun when it would be a red giant?

texts:
In about 5 billion years the Sun is predicted to become a red giant and have more than 200 times its current size, reaching a radius of about 5 AU when largest.

I wonder what spectral class the Sun would have then, I think somewhere from M1III to M5III. Do we know a red giant star that is similar to what the Sun is predicted to become?


texts:
According to Wikipedia, re Europa's tidal flexing:

  the tidal flexing kneads Europa's interior and gives it a source of
  heat, possibly allowing its ocean to stay liquid while driving
  subsurface geological processes.The ultimate source of this energy is
  Jupiter's rotation, which is tapped by Io through the tides it raises
  on Jupiter and is transferred to Europa and Ganymede by the orbital
  resonance.

https://en.wikipedia.org/wiki/Europa_(moon)

Does this imply that Jupiter's rotation is slowing over time, since it is losing energy due to raising tides on Io?  (Or just generally, does raising tides cause rotation to slow?)


texts: Has radio astronomy ever been done on objects that appear very close to the Moon? Is this avoided?

texts:
This answer to Which kinds of astronomical observations most need to avoid the Moon being up? mentions

  For completeness - radio, mid-infrared and mm-wave observations are unaffected (unless the Moon is in the way!)

The Moon is of course opaque to all wavelengths used in astronomy, from very low frequency radio waves to gamma rays. So if the moon eclipses a target radio signals will be blocked.

But are there any more subtle or non-obvious effects? For example if a target is very close to the Moon but not covered by it, would that affect an observation in any way?

Question: Is this routinely avoided out of an abundance of caution? On the other hand, has a lunar occultation of a radio source ever be leveraged in some way for a specific measurement?

"Bonus points" for any anecdotes of strange results or confounding measurements in Radio Astronomy that turned out to be the result of not taking the position of the Moon in to consideration.


texts: Is it possible to have a trinary star system with a planet that orbits their barycenter?

texts:
I am trying to model a 3-star system with a planet. The three stars have the same mass. I have gotten the stars (Yellow, Pink, Blue) into a stable orbit. However, I am wondering if a "free-floating" planet can exist in this system. By "free-floating," I mean a planet that does not orbit any star; it orbits the barycenter.
Currently, I only know of metastable orbits that work for a while, but then the planet crashes into a star or gets ejected. Here are my setups:

Is there such a system that satisfies these conditions? If yes, is there a real-life example that astronomers know of?

There are 3 stars of the same mass.
There is a planet that orbits the barycenter of these three masses.
The planet is orbiting in a "Hot Jupiter" setup (the planet orbits close to the barycenter)


texts: Convert RGB pixel value of an image to limiting magnitude

texts: I have taken photos at different exposures from different places of the Orion constellation. I wish to find the effect of skyglow on the limiting magnitude of stars in the Orion constellation. How can I estimate the limiting value of any star from its RGB pixel value in the photograph?


texts: Do magnetic fields affect planetary rings?

texts: Planetary rings seem to generally form on the ecliptic plane because of the rotation of the planet, but I was wondering what kind of effect the magnetic field of the planet might have on the ring system. Would it help keep the ring system together, disrupt it, or have little to no effect? What if the magnetic poles were on or near the ecliptic?


texts: Can there be an infinity of stars in the Universe?

texts:
I have a mind puzzle.

Can there be an infinity of stars in the Universe ?

I have 2 opposed reasonings, yet I don’t find any flaw in them. Can you help me here ?

Answer A : No, the number of stars cannot be infinite.

In the whole Universe, at an instant t, there are W molecules of water. This number may be very big, but it has a definite value. The same goes for stars. Each of all the stars at the instant t has her own size, and we can give her a name. We can list all of them, and we can sort them from nearest to farthest — if we are omniscient, of course.

Answer B : Yes, the number of stars can be infinite.

Space has no finite volume. Space has no ending wall. If I advance into space, I can always go further. Wherever I go, space is by default filled with… vacuum. But it could be otherwise. [I am not sure of this point.] Space could be by default filled with… air. So there would be +∞ molecules of air in the Universe. We can apply this reasoning to stars. Let’s say there is, in average, 1 star / 1060 m3. So, in the total infinite volume of space, there would be +∞ stars. When I advance into space, I would keep meeting new stars, without end. Like in these video games in which mountains keep appearing as far as you walk.


texts: What's the critical mass of a rocky planet before its gravity traps enough gas in its atmosphere to start becoming a gassy planet

texts:
Looking at the latest theories, I've noticed that most rocky planets are below a certain mass range. I speculate that maybe the way gas giants and gas dwarfs form is a rocky planet during the planetary formation phase of its history accumulates enough mass to begin gaining a hydrogen atmosphere that keeps building until it's no longer a rocky planet.
What would be the critical mass of a rocky planet before it would start down the path of becoming a gassy planet?


texts: Is a trefoil orbit around a trinary star valid?

texts:
Recently, I have been experimenting with weirdly-shaped orbits with a program called "My Solar System 2.04." While looking for interesting orbits of a spacecraft in a trinary star, I found an type of quasi-orbit called of a trefoil, as shown in this clip. Is this orbit possible in real life, and are there any examples of them that we know of?
Edit: The objects in the video are color-coded.


texts:
I would like to fit planets orbits. To do this, I need a set of mock observations. I can get them from right ascension/declination obtained from the Horizons interface:

EDIT:
Horizons gives me a list {time,right ascension [hms],declination[dms]}. I need to reconstruct at least one observed orbit, for example of Mercury, around the Sun. My confusions is: how to convert the output coordinates from Horizons? Is it sufficient to convert them from equatorial to ecliptic?
Is there any suggestion to implement the correct procedure?
EDIT 2:
I changed the settings in Horizons in this way

To have {X,Y,Z} in AU and the Sun as body center. Then I tried to overlap simulated orbit with Newton's equation with the horizons coordinates.
Is this the right way to make the coordinates comparable for a fit?


texts: Can a photon have a stable orbit around a black hole?

texts:
Can a black hole free from an accretion disk collect photons in the photon sphere in a prolonged stable orbit?

Could enough photons be in orbit to shade the actual black hole with light?

Would a rogue black hole appear to have an atmosphere made of photons from the light emitted from other distant stars entrapped and released?


texts: Does the Honey moon have a precession problem?

texts:
In Steven Colbert's interview with Neil deGrasse Tyson after about 03:16 the following is explained:

But wait, all the moons - all the full moons of the year have names. Some are familliar like the Harvest moon… and the Moon in June never gets too high in the sky, so it takes on sort-of an amber sunset color, the whole trip. And so that's called the Honey moon. So the June full moon is the Honey moon.

Is there a problem here though? For any given month won't the full Moon oscillate between low and high above the horizon at midnight on an 18.6 year cycle?
Video: Is An Asteroid Going To Hit Earth On Election Day? Neil deGrasse Tyson Says Maybe


texts: Why do massive stars not undergo a helium flash

texts: I understand that for low-mass stars the helium flash occurs due to their degenerate helium cores. Thus the answer to this question is probably that more massive stars do not have a degenerate core, but I do not understand why they wouldn't. Due to their increased mass, I'd assume their central pressure is even higher, so surely their cores should also be degenerate?


texts:
I know the latitude and longitude of a city ($41^\circ 87'$ N, $87^\circ 62'$ W), the declination and right ascension of a star($16.51^\circ$, $68.98^\circ$) and the local time, date (27.12.2017, 1:20 AM). Could you please show me the exact calculations for hour angle, altitude?

I will use the formula $LST=100.46+0.98d+15UT$, where d is the number of days since 1.1.2000 at 00:00 and UT is the universal time.

At 1:20 AM, $d=6570.055$.

UT is $UT=7:20$ or in hours $UT=7.3$.

$LST=6648.0639$ or $LST=168.0639$

$HA=LST-RA=168.0639-16.51=151.5539$

How is my calculation?


texts:
There's no way around it: when I look at the full moon at night it looks like a mostly flat disc, with at most a bit convexity in the middle. Phases of moon look like a full moon seen through a cut-out.

Why is that the case? I recall, when I was really young, looking at it through what at the time seemed to be a very strong telescope, and it appeared not only a lot more textured but also a lot rounder. A similar thing can be seen in a video I saw a couple months ago, at 2:05: https://www.youtube.com/watch?v=XCrJ3NflOpE . So it's clearly a naked eye thing.

I presume it's related to the optics, which made me hesitant to post it on this stack exchange (thinking it might be more suited to the physics one), but chose against it presuming people here would have more experience with celestial bodies and "large" distances.

I have a hunch that the answer is very simple, but I really don't know what that might be, especially since it's done over what I view as large distances.


texts:
When (yyyy-mm-dd) does the north pole of uranus most nearly point towards the sun?
The information I've found suggests this happened in 1944 or 1945, but would like to find a more precise date or alternately what the heliocentric longitude is.
The "Poles of Astronomical Bodies" article on Wikipedia lists the RA and Dec, but doesn't include the Geocentric distance (otherwise, I think I could just translate between geocentric and heliocentric coordinate systems and have my answer).
Thanks
Tim


texts: What effect does Earth losing a part of its mass have, is there an impact on the Earth's orbit around the Sun?

texts:
This is a random question that popped into my mind. I'm not a physicist or astronomist, however, I am genuinely curious. Also, this is not intended as a science fiction question, but an actual science question.

I had doubts about where this question should be posted - the Astronomy or the Physics SE page, in the end, I decided to post it here.

Sub-questions that I have, all being closely related to the one in the title:

Do the liftoffs of spaceships have any impact on Earth's orbit? As negligible as they might be?
Every bit of mass lost (sent into space) decreases the gravity of our planet, as tiny as the change might be. Is that correct?
Could the loss of Earth's mass over time (Hypothetically - centuries in the future, with tens of thousands of spaceships having left Earth.) change the orbit of Earth or produce any side-effects?


texts: Deriving the first moment of Collisionless Boltzmann Equation in Spherical Polar Coordinates

texts:
I am following these notes: Dynamics and Astrophysics of Galaxies.
After equation 6.37, we have:
\begin{equation*}
    p_r\,\frac{\partial f}{\partial r} + \frac{p_\theta}{r^2}\,\frac{\partial f}{\partial \theta} +
    \frac{p_\phi}{r^2\,\sin^2\theta}\,\frac{\partial f}{\partial \phi}
    -\left(\frac{\mathrm{d} \Phi}{\mathrm{d} r}-\frac{p_\theta^2}{r^3}-\frac{p_\phi^2}{r^3\,\sin^2\theta}\right)\,\frac{\partial f}{\partial p_r}
    +\frac{p_\phi^2\,\cos\theta}{r^2\,\sin^3\theta}\,\frac{\partial f}{\partial p_\theta} = 0\,.\\
\end{equation*}
This is the Collisionless Boltzmann Equation in Spherical Polar Coordinates.
Then

We now multiply this by $p_r$ and integrate over all $(p_r,p_{\phi},p_{\theta})$ using
that $\mathrm{d}p_r\,\mathrm{d}p_\phi\,\mathrm{d}p_\theta = r^2\,\sin\theta\,\mathrm{d}v_r\, \mathrm{d}v_\phi\,\mathrm{d}v_\theta$ and using partial integration to deal
with the derivatives of f with respect to the momenta

\begin{align}\label{eq-spher-jeans-penult}
    \frac{\partial (r^2\,\sin\theta\,\nu\,\overline{v^2_r})}{\partial r} + \frac{\partial (\sin\theta\,\nu\,\overline{v_r\,v_\theta})}{\partial \theta} & +
    \frac{\partial (\nu\,\overline{v_r\,v_\phi}/\sin\theta)}{\partial \phi}\\
    &
    +r^2\,\sin\theta\,\nu\,\left(\frac{\mathrm{d} \Phi}{\mathrm{d} r}-\frac{\overline{v_\theta^2}}{r}-\frac{\overline{v_\phi^2}}{r}\right) = 0\nonumber\,.
\end{align}
I would like to arrive to this result myself. Multiplying the SPC CBE by $p_r$ & going ahead with the suggested volume element, considering the first term in the above equation, not being worried about the integration limits gives us:
\begin{equation}
\int p_r \frac{\partial f}{\partial r} p_r r^2 \sin\theta \mathrm{d}v_r \mathrm{d}v_{\theta} \mathrm{d}v_{\phi}
=\int v_r^2 \frac{\partial f}{\partial r} r^2 \sin \theta \mathrm{d}v_r \mathrm{d}v_{\theta} \mathrm{d}v_{\phi}
=r^2 \sin \theta \int v_r^2 \frac{\partial f}{\partial r} \mathrm{d}v_r \mathrm{d}v_{\theta} \mathrm{d}v_{\phi}
\end{equation}
Using 6.32 from the mentioned notes,
\begin{equation}
\frac{\partial (r^2\,\sin\theta\,\nu\,\overline{v^2_r})}{\partial r} = \frac{\partial}{\partial r} \left( r^2 \sin\theta \int v^2_r f \mathrm{d}v_r \mathrm{d}v_{\theta} \mathrm{d}v_{\phi} \right)
\end{equation}
Which is not equal to what I have found just a line above.
What am I doing wrong?

Some question on Math.SE & Physics.SE.


texts: Recently a Galaxy was discovered that contained no Dark Matter. I was wondering what explanation could be offered for this ? This Galaxy also contains only 1% as many Stars as our Milky Way does . Is there be a connection between these two things, lack of many Stars and lack of Dark Matter ?


texts: A clock travelling "faster than the speed of light"

texts:
When a clock travels close to the speed of light as observed by us, it should tick slower.

Does this mean that, when using this clock to measure a second - it could travel much more than 300 000 km during a second? In fact, this clock could travel infinitely fast when viewed only from its own perspective?

Does this imply that if I traveled on a space ship, at the speed of 99 % of light, I would age 4 years, but could reach a destination perhaps 400 light years away?

My friends and family on earth would have perished, but the people I saw on the destination planet as I started my journey will have aged only 4 years as well.

If the last assumption is correct; it means that we could watch a launching space ship at alpha centauri, it could arrive here in just 3-4 days - appearing to travel much faster than the speed of light, without breaking the laws of relativity. We would just say that it was relativistic blue shift that made it seem to travel faster than the speed of light.


texts:
I know that we don't see green stars because in blackbody radiation star doesn't produce one spectrum.

The stars that have peaks in the green spectrum produce other spectrum in nearly same amout. This make them appear white.

If stars have peaks in the infrarad spectrum that has wavelength little longer than red.

We see those stars red because they produce red spectrum more than other visible spectrum.

But if stars have peaks in the ultraviolet spectrum that has wavelength little shorter than violet. Why don't we see those stars purple ?


texts: Do telescopes exist that reflect the incoming light more than three times along their length?

texts:
Refractors only use the length of the telescope once, reflectors twice, catadioptric telescopes like those of the Schmidt-Cassegrain design three times. Have telescopes been built that reflect the incoming light at least once more from one end of the telescope to another?

Say, by adding a tertiary mirror which reflects the light forward again, towards a small quarternary mirror in front of the secondary, which ultimately directs the light though a small hole in the tertiary (and primary) mirror towards the eyepiece?
Note: The above description makes this question different from the similar-sounding Do triple or more times reflecting telescopes exist?


texts: How is it determined that the X-ray and radio intensity come from a magnetic field bridge between two clusters of galaxies?

texts:
Gizmodo's Astronomers Spot Mysterious, 10-Million-Light-Year-Long Magnetic Field Connecting Two Galaxy Clusters shows the image below, and Space.com's A Weird 'Radio Bridge' 10 Million-Light Years Long Links Colliding Galaxy Clusters discusses it as well.
They both link to the new paper in Science A radio ridge connecting two galaxy clusters in a filament of the cosmic web (also arXiv).
What I've gathered so far is that seen between two known and characterized clusters of galaxies, there is a region with some excess continuum radio power at 140 MHz and some excess continuum X-ray power.
Neither of these are spectral features so their distances can't be associated with the galactic clusters by doppler shift.
Question: How do they know that the X-ray and Radio continuum are both really coming from the space between these two clusters of galaxies, and not in front of or behind it?
"bonus points" how does Planck's "y parameter" figure in to this mix?

“A radio ridge connecting two galaxy clusters in a filament of the cosmic web”, F. Govoni et al. 2019, Science. Optical: DSS and Pan STAARS (insets) — Red, X-rays: XMM-Newton — Yellow, y-parameter: Planck satellite — Blue, radio 140 MHz: LOFAR. Image credits: M. Murgia - INAF
The two galactic clusters and the intervening radio ridge. Image: DSS and Pan-STARRS1 (Optical), XMM-Newton (X-rays) PLANCK Satellite (y paramter), F. Govoni, M. Murgia, INAF


texts: Are epicycles and mean Earth/Sun actually useful astrophysical concepts?

texts:
Copernicus put the Sun in the center of the Solar system. This turns the Moon's orbit into an epicycle around Earth orbit. And the Jovian moons (later discovered) have orbits which are epicycles around Jupiter. Since Copernicus created a physical epicycle in the Moon, it maybe wasn't so strange to think about "epicycles of epicycles" as he did to improve the model's fit to calendar data.

Actually, Ptolemy and Brahe did not put Earth in the center of their Solar system models. They used a fixed point in empty space near the Earth which they called "mean Earth". And Copernicus used a corresponding "mean Sun". And as a matter of fact, planets do turn around a barycenter which is not in the center of the Sun, but nearby.

Do epicycles and "mean Earth/Sun" actually have physical correspondents in the orbits of moons and the barycenter respectively? That'd be a bit funny since they are purely geometric constructions with the purpose to make data fit better, created even without a thought about gravity or anything physical at all.


texts: Do planetary radio frequency change upon alignments?

texts:
If Neptune would align Uranus, would the radio frequency perceived on Earth increase?

Are the radio antennas on NM capable of getting the 2 different radio frequencies feom both planets or would they get a bigger range of frequencies?


texts: How do I measure occultation for the upcoming lunar eclipse?

texts:
I'm trying to simulate the lunar eclipse on Jan. 31, similar to this simulation I made of last year's solar eclipse, using Three.js. I have the minute-by-minute coordinates for the Sun and the Moon in the J2000 frame -- where Earth is always at [0,0,0] -- and need to calculate the degree of occultation at each moment.

I'm treating the Sun as a point, since that's how 3D lighting works in Three.js, and came up with what I think is a clever solution to account for the penumbra: I calculated what size the Earth would have to be to create the penumbra from a point instead of a large spherical light source, like so:

(This obviously isn't to scale, but the inner circle would be the actual earth, the black lines are the penumbral rays from the Sun, and the blue lines originate from the center of the sun but reach the plane of the moon (the little gray guy) at exactly the same point.)

To test whether this actually works, I need to calculate the occultation of the moon and my imaginary Penumbral Earth (which is 8154.15km in radius), and compare those figures to Fred Espenak's calculations.

I found this StackOverflow post on how to calculate the angle between two vectors in 3D space. What I can't figure out his how to determine the apparent width of that angle and whether it is greater than the sum of the apparent radii of the Earth and Moon. I thought the Law of Cosines would be sufficient, but it accounts for the distance between the Earth and Moon as well. Here's a to-scale simulation showing the path of the moon over 24-hours on Jan. 31, with the Sun way off-screen:

One idea I had was to measure the vector from the sun to the outer edge of the fake earth, and the vector from the sun to the inner edge of the moon, but cannot figure out how to determine the points on the sphere where these vectors would be tangent. (I posed this question to Math StackExchange, but am hoping there's an easier way.)

While SPICE (via the Python wrapper spiceypy) was perfect for getting the locations of the bodies, it's occultation function doesn't allow for an arbitrary location of the observer, which eventually I will need to account for.

Is there an easy--or difficult--equation for occultation? Thanks!


texts: I know Seyfert galaxies are types of active galaxies, but I do not understand what separates them from other types of active galaxies.  Are they brighter/not as bright as other types of active galaxies?  Do they emit in different wavelengths relative to other active galaxies?  I've read that 10% of all galaxies are Seyfert galaxies, so it seems to me that understanding what these galaxies are is very important to understanding galaxies overall.


texts:
They actually do, but let's set Relativity aside for a moment. And the whole barycenter thing too. Here's the scenario:

Somewhere in the backwaters of a galaxy there is this huge planet. It is NOT a failed star. It could be considered a gas giant, except most of the gas is nitrogen, with traces of oxygen. The planet has a nucleus with a rocky surface covered in part by water. There's life on the planet, maybe even intelligent life. Orbiting this planet is a dwarf star. It is sufficiently close to the planet to provide energy and warmth, and not close enough to incinerate it. Its orbital speed is sufficient to warm the equatorial parts of the planet without singing them when it passes over them and to come back to them before they freeze over. Or maybe there are two stars of slightly different sizes, traveling along different orbits.

Is this at all possible?


texts: Does our universe have to be embedded in a higher dimensional space?

texts: I've heard that our universe may be open or closed.  If it's closed it might have a toroid shape.  If this is the case, would that imply that our 3 spatial dimensions have to be embedded in a higher dimensional (spatially) space?  For example, the old asteroids video game was apparently a torus mapped to a 2-dim video screen, and it stayed in 2 dimensions, but with a specific behavior of moving objects.


texts: How can I crop a fits file and get correct WCS header info without a new plate solve and WITHOUT USING PYTHON?

texts:
While my question is similar to this one, the suggestions offered there won't work for my specific situation.  For over a month I've been trying to find software capable of this but it's been an unsuccessful search.  I don't think the software exists; however, I haven't asked this group yet. I sure hope I'm wrong.
The Problem

if I crop a fits image, the WCS is lost (which makes sense, the image has changed) but the cropping software won't recompute the WCS for the new area and add it back into the new header

The Data Set

a collection of .fits image files created by a CCD (not tables or any
other kind of .fits file)
each individual image is large in terms of degrees of sky
minimum number of files in set: ~1,150 and max number is: ~15,000
each image has the WCS info in the header
each image is registered on a sub pixel level to the others

Software Requirements

IS NOT PYTHON unless it has a GUI interface hiding all evidence of Python code
runs in local Windows environment, not cloud based
works in a batch or bulk mode
copies the header from the original but updates the WCS entries
updates the other headers as necessary such as NAXIS1

Additional info: why standard methods don't work

the images can't be plate solved by astrometry dot net (they are very out of focus (on purpose with a diffuser) or the plate scale is extreme at over 20 arc-secs per pixel which looks out of focus but isn't)
while the crop with WCS update could be done in Python, this project requires a GUI

I've tried SAOimageDS9, AstroImajeJ, PixInsight, Mira, and MaxIm DL 6 Pro but they don't recompute the WCS entries. My goal is to create a procedure to do aperture photometry on special data sets without using Python but first I need to determine if it's possible.  A crop is required before all else due to the size of the data.
When working with other data sets, cropping issue isn't a problem.  The images are registered, then the crop is performed (as well as any 'rotate 180 deg' or mirror left/right/top/bottom).  It removes the WSC headers but plate solving the new, smaller, postage stamp image puts the corrected ones back in.
If anyone knows of software to crop fits images and return correct WCS headers, it would help tremendously.


texts: Moment of inertia factor of Venus and Pluto

texts:
Wikipedia's Moment of inertia factor begins:

In planetary sciences, the moment of inertia factor or normalized polar moment of inertia is a dimensionless quantity that characterizes the radial distribution of mass inside a planet or satellite. Since a moment of inertia must have dimensions of mass times length squared, the moment of inertia factor is the coefficient that multiplies these.

The article lists values for 18 solar-system bodies including the Ceres and many moons.
But Venus and Pluto are conspicuously absent from this table.
What are the RI factor values for Venus and Pluto? Is there any source of reasonable calculation done for these two?
C/MR2
According to this note on the page Venus has a range of 0.327–0.342. Pluto is not mentioned anywhere.


texts: What is the likely closest encounter for a typical star during the Milky Way Andromeda Merger?

texts:
This is closely related, but distinct question to What are the chances of a star colliding with another during a galactic collision?.

The accepted answer to that question places the odds of the Sun colliding with another star at about $10^{-12}$, what I want to ask is how near a near-miss is expected? In other words, what is the expected closest encounter between the Sun and another star during the collision? A more sophisticated answer would give the expected distribution of close encounters by distance.

A more general version of the question is -- what disruptive events would a typical star such as the Sun expect to experience during the merger?


texts: When the asteroid hit the earth 65 mya did the earth's gravity pull change? By how much?

texts: When the asteroid hit the earth 65 million years ago, did the earth's gravity pull change? By how much?


texts: Could someone see anything while being inside black hole?

texts: If we managed to survive in a black hole and move inside the event horizon then could we see the surroundings of the black hole inside the event horizon by source of light? Can the light not come up to the event horizon or does it have to travel through different spheres of the black hole and enter a sphere which won't allow the light to return to its previous sphere? If the we reach up to the singularity then can we ever reach up to the event horizon or would we get stuck in the point of the singularity?


texts: How to tell which of the ecliptic cross horizon angles is to the east?

texts:
Jean Meeus' Astronomical Algorithms, 2nd ed. p. 99 gives a formula for finding the two longitudes where the ecliptic crosses the horizon:

$$\tan\lambda = \frac{-\cos\theta}{\sin\epsilon \tan\phi + \cos\epsilon\sin\theta}$$

where "$\epsilon$ is the obliquity of the ecliptic, $\phi$ is the latitude of the observer, and $\theta$ is the local sidereal time, returns $\lambda$ the longitudes of the two points of the ecliptic which are (180 degrees apart) on the horizon".

The software I am using then applies $\arctan$ to get $\lambda$ and adds $\pi$ if $\lambda < 0$. Then it returns $\lambda$ and $\lambda + \pi$.

I need to know which of the two angles returned points to the easterly direction. Is there any way to tell which is which? I have all of the information needed to perform the calculation (UT, local time, sidereal time, latitude, longitude), but I can't see how they are related.

Thanks much!